Particle beam therapy damages a diseased tissue by particle beam irradiation to perform treatment and is one of radiation therapies in a broad sense. A particle beam such as a proton beam and a heavy ion beam, unlike other radiation such as a Y-ray and an X-ray, is capable of adjusting the depthwise irradiation dose position depending on the energy of the particle beam, thus allowing for imparting dose in accordance with the three-dimensional shape of a diseased site. An accelerator is used for generating a particle beam of prescribed energy.
The accelerator is made up of bending electromagnets for forming the orbital path, an accelerating cavity for accelerating the particle beam by means of a radio frequency electric field, a vacuum duct that is a path through which the particle beam travels, and others. As the particle beam is accelerated (increases in energy), the magnetic fields of the bending electromagnets are varied in accordance with an operation pattern predetermined by reflecting the design and the result of beam adjustment. Since the orbital frequency also varies at the same time, stable acceleration needs the radio frequency signal applied to the accelerating cavity to be also controlled in its frequency and amplitude (intensity) in accordance with the predetermined operation pattern. The operation pattern needs to be changed according to the energy of the particle beam to be extracted. The accelerator further includes an extraction electrode and an extraction electromagnet as devices for extracting from the accelerator the particle beam accelerated and reached the prescribed energy. The extraction electrode is for deviating the path of the particle beam reached the prescribed energy from the orbital path to the extraction path by action of the electric field, and the extraction electromagnet is for deflecting the particle beam on along the extraction path to extract the beam externally from the accelerator. Settings of these extraction electrode and extraction electromagnet need to be changed according to the energy of the particle beam to be extracted.
The particle beam extracted from the accelerator is delivered through a beam delivery line to a particle beam irradiation apparatus for irradiating a patient. The beam delivery line includes devices such as bending electromagnets for bending the particle beam path along the delivery line and electromagnets for controlling divergence and convergence of the particle beam. Moreover, the particle beam irradiation apparatus includes devices such as electromagnets and a ridge filter. Setting of these devices needs to be also changed according to the energy of the particle beam to be extracted as with the extraction electrode and the extraction electromagnet.
An irradiation method for particle beam therapy is roughly classified into a broad irradiation method in which the whole diseased site of a patient, which is an irradiation target, is irradiated in one time with a particle beam and a scanning irradiation method in which the diseased site is scanningly irradiated with a particle beam. In the broad irradiation method, the irradiation particle beam has a fixed energy. In the scanning irradiation method, in contrast, the particle beam is varied in energy to irradiate a wide range in the depth direction. The energy of the particle beam is varied by changing the operation patterns of the accelerator magnetic fields and of the radio frequency. Hence, in the scanning irradiation method, the operation pattern of the accelerator needs to be set correspondingly to each energy and intensity of the beam.
A file compiling the operational parameters for each device of the accelerator is referred to as an operation file (hereinafter, abbreviated as “OPF”). The accelerator, when reads the OPF in, repeats the operation pattern in the OPF. In the scanning irradiation method, operation is performed while switching the OPF for each pulse (for each spill). This is referred to as pulse-to-pulse operation (abbreviated as P-to-P operation).
An operation pattern, a timing, and the like for a P-to-P operation are disclosed in, for example, Patent Document 1, Patent Document 2, Patent Document 3, and the like.